This invention relates generally to wide area vacuum ultraviolet (VUV) light sources that are disc-like in shape and more specifically to such a light source that is created by employing a ring-shaped abnormal glow discharge electron gun that produces a flat disc-shaped trapped electron beam generated plasma.
Photo-exposure, decomposition, and cross-linking of polymer materials all require a VUV light source of wide area. In addition, photo-assisted chemical vapor deposition, etching, and growth of organic or inorganic based microelectronic, photovoltaic, and electro-optic films also require a wide area VUV light source of disc-like geometry to promote rapid low temperature processing of materials in such a way that they remain free of plasma radiation damage. Photodeposition of hydrogenated amorphous silicon requires a VUV light source, for example, when using monosilane as a feedstock gas. There is a strong need for VUV light sources in all of these applications and many others. Of special interest are wide area VUV lamps providing a source of photons as well as a source of ground state and excited atomic species. Sensitized atommolecule reactions can both dissociate feedstock gases and may assist heterogeneous surface reactions.
Conventional VUV light sources include both high pressure and low pressure gas discharge lamps. Enclosed low pressure mercury-xenon lamps and high pressure xenon arc lamps have both been employed as VUV light sources. These lamps are excited by either a radio frequency or D.C. electrical source. A VUV transmitting window is necessary for such lamps. A VUV lamp usually requires special window materials, such as MgF.sub.2, LiF, sapphire, CaF.sub.2 to transmit VUV resonance light. The window material is often hydroscopic, degrades its VUV transmission with time, and is expensive to replace. Removal of the more intense infrared/optical spectra can be achieved via wavelength filtering of the output radiation from such enclosed lamps.
Conventional VUV light sources also include hollow cathode lamps with or without VUV windows. Such hollow cathode lamps are usually cylindrical rather than disc-like lamps and have a small circular area (&lt;3 cm.sup.2). The hollow cathode lamp has the ability to generate a self-contained and localized discharge. That is, it can operate within a microelectronics processing chamber without exciting a large and diffuse volume plasma within the chamber. However, the hollow cathode is a closed wall structure that substantially prevents ouldiffusion of atomic species created in the plasma region. Moreover, substantial undesired cathode sputtering occurs in the hollow cathode.
Conventional lamps then (with the exception of hollow cathodes) employ both VUV windows and enclosure wall to maintain the specific lamp gases at the required pressure within the lamp. The need for a VUV window having a high optical transmission chrracteristic, the additional need for a source of excited atomic species, and the creation of wide area illumination of disc-like geometry in the VUV spectral region are all major problems associated with conventional VUV lamps. VUV lamps having diameters equal to or greater than 2-5 centimeters are simply not possible using previous gas discharge methods described above. Conventional enclosed VUV lamps are limited in circular area to dimensions less than several square centimeters. Hence, they can directly illuminate only a portion of a 5 centimeter to a 20 centimeter diameter substrate used in silicon or III-V microelectronics manufacture as well as in large area solar cells or flat panel displays.
Conventional enclosed VUV lamps using D.sub.2 or H.sub.2, for example, as a gaseous medium only create VUV radiation. They do not create and allow atomic hydrogen or atomic deuterium to diffuse unimpeded from the lamp plasma into the region between the lamp and the substrate. Conventional enclosed VUV lamps have closed wall structures that inhibit or prevent the diffusion of atomic fragments from the localized plasma region into the microelectronic processing chamber, especially over a wide area. Conventional lamps have walls and windows that are not open in structure as is the case for the ring cathode structure taught in accordance with the present invention. Hence, diffusion of atomic species from the plasma cannot occur over a wide area, if at all, for closed wall conventional VUV lamps. These atomic species can be used in sensitized atom-molecule reactions to cause dissociation of the feedstock reactant gas phase molecules used in microelectronic, photovoltaic, and electro-optic films or to assist surface reactions on substrates.